Many differential pressure gauges are of the
conjunction with signal conditioners. Transducers
bellows type. In some designs, one pressure is
provide the capability of sensing variable pressures
applied to the inside of the bellows and the other
and transmitting them in proportional electrical
pressure is applied to the outside. In other designs,
signals. Pressure transducers, like pressure
a differential pressure reading is obtained by
switches, are widely used in ship propulsion and
opposing two bellows in a single case.
auxiliary machinery spaces. They are used to
Bellows elements are used in various applica-
monitor alarms and in machinery operation.
tions where the pressure-sensitive device must be
powerful enough to operate not only the in-
Pressure Transducer Operation
dicating pointer but also some type of recording
device.
Pressure transducers are generally designed to
sense absolute, gauge, or differential pressure.
ELECTRICAL PRESSURE MEASURING
The typical unit (fig. 5-18) receives pressure
INSTRUMENTS (TRANSDUCERS)
through the pressure ports. It transmits an
electrical signal, proportional to the pressure
Transducers are devices that receive energy
input, through the electrical connector. Pressure
from one system and retransmit it to another
transducers are available in pressure ranges from
system. The energy retransmitted is often in a
0 to 6 inches water differential to 0 to 10,000 psig.
different form than that received. In this section,
Regardless of the pressure range of a specific unit,
we will discuss the pressure transducer. This device
the electrical output is always the same. The
receives energy in the form of pressure and
electrical signal is conditioned by the signal
retransmits energy in the form of electrical
conditioners before being displayed on an analog
current.
meter or a digital readout located on one of the
Transducers allow monitoring at remote
control consoles.
locations on gas turbine propulsion plants.
Mechanical gauges provide pressure readings at
Pressure Transducer Calibration
the machinery locations or on gauge panels in the
immediate area. At a central location remote
Pressure transducers should be calibrated on
readings are provided by using transducers in
a bench before installation. The equipment needed
Figure 5-18.--Pressure transducer assembly.
5-13
